1. Field of the Invention
This invention relates in general to the field of gravel packing and stimulation systems for mineral production wells, and more particularly, to an improved method and system for performing gravel packing and stimulation operations. The present invention also relates to the completion of wellbores in the field of oil and gas recovery. More particularly, this invention relates to an improved apparatus adapted to provide a method of performing multiple downhole operations, such as gravel packing and stimulating/servicing in a single trip. The present invention also relates to a method of providing stimulation or treatment fluid through a gravel pack or gravel pack screens such that filter cake can be effectively removed from the wellbore. More particularly, the invention relates to a method for providing mechanical energy of high pressure rotating jets to force the stimulation or treatment fluid through the gravel pack screens, thus creating a mechanical diversion to remove the filter cake, without damaging the gravel pack.
2. Description of the Related Art
In an effort to extract natural resources such as oil and gas, it is becoming increasingly common to drill a vertical well, and to subsequently branch off that well and continue to drill horizontally for hundreds or even thousands of feet. The common method for drilling horizontally will be described more fully below, but generally includes the steps of forming a fluid impermeable filter cake surrounding the natural well bore while drilling at the production zone, removing drilling fluid from the downhole service tools (washdown), performing gravel packing operations, and then removing the downhole service tools from the well bore. A stimulation tool is then run back into the well, and the well stimulated with the appropriate chemicals to remove the filter cake so that production may begin. The above-described method requires two “trips” down into the well bore with different tools to accomplish gravel packing and well stimulation. Each trip into the well can take as much as a day, with the cost of a rig running anywhere from $50,000.00 to $250,000.00 per day. Accordingly, achieving both gravel packing and stimulation in a single trip can be substantially beneficial. Further, each additional trip into the well also increases the risk of fluid loss from the formation. Fluid loss in some cases may substantially reduce the ability of the well to effectively produce hydrocarbons. Therefore, there is a need for a system and method that simply and reliably performs gravel packing and stimulation operations in a single trip into the well.
The drilling of horizontal wells is becoming increasingly common in an effort to extract natural resources such as oil and gas. In horizontal wells it is common practice not to form a casing in the wellbore along the portion of the horizontal wellbore through which oil or gas is to be extracted. Instead, during drilling operations a filter cake is deposited on an inner surface of the wellbore. This filter cake is typically a calcium carbonate or some other saturated salt solution that is relatively fluid impermeable, and therefore, impermeable to the oil or gas in the surrounding formation. The filter cake is formed during drilling by pumping a filter cake slurry having particles suspended therein into the wellbore. The particles are deposited on the wellbore surface, eventually forming a barrier that is sufficiently impermeable to liquid. Systems and methods for depositing such a filter cake are well known in the art. I
With the filter cake in place, the drilling equipment is removed from the well, and other tools are inserted into the well to pack the well with gravel. Once gravel packing is complete, the filter cake must be stimulated with the proper chemical solution to dissolve the filter cake to maximize production flow into the well. Further, some companies only stimulate injectors; such that filter cake can be produced through the sand and screen but cannot be effectively pumped into the wellbore. Typical prior art systems and methods require removal of gravel packing tools and subsequent insertion of stimulation tools.
The steps of placing the filter cake, gravel packing, and stimulation are often utilized with horizontal wells. A common method for drilling horizontally generally includes forming a fluid-impermeable filter cake surrounding the natural well bore while drilling at the production zone, removing drilling fluid from the downhole service tools (washdown), performing gravel packing operations, and then removing the downhole service tools from the well bore. In a second operation, a stimulation tool is then run back into the well, and the well stimulated with the appropriate chemicals to remove the filter cake so that production may begin.
The above-described method requires two trips down into the wellbore with different tools to accomplish gravel packing and well stimulation operations. Each trip into the well takes time, thus increasing the costs of performing the operations. Each trip also increases the risk of fluid loss into the formation. Thus, it is desirable to perform both the gravel packing operation and the stimulation operation in a single trip. According to the present disclosure, however, a single tool assembly can be lowered into the well to perform both gravel packing and stimulation in one trip.
Some methods for performing the gravel packing operation and stimulation in a single trip, such as U.S. application Ser. No. 10/095,182 to Walker, incorporated by reference herein as described above, utilize seal subassemblies in conjunction with slick joints in some embodiments. The slick joints may be sized to mate with the plurality of seal subs, such that layers downhole may be isolated. Such methods may be utilized to stimulate horizontal wellbores in a layer-by-layer, screen-by-screen fashion. As is known in the art, the seal subs are spaced such that the seal subs cooperate with the slick joints to selectively seal a given stratification layer downhole. By pulling upwardly on the workstring, a different stratification layer is isolated. Such systems utilize given slick joints for cooperation with a give wellbore, such that the slick joint cooperates with a plurality of seal subs to isolate given zones.
It is desirable to provide a single trip system, which may be utilized without utilizing the slick joint/seal sub combination, and thus eliminating the sizing of the slick joints/seal subs. Such a system would advantageously be able to stimulate a plurality of production screens as the tool is pulled out of hole, in a continuous—as opposed to performing a layer-by-layer stimulation—operation. Further, such methods perform the stimulation operation sequentially through layers lying along production screens. It is also desirable to utilize a pressure pulsating rotating jetting tool to improve the stimulation operation downhole.
Embodiments of the present invention are directed at overcoming, or reducing and minimizing the effects of, any shortcomings associated with the prior art.